It is well known that the speed of an Otto or Diesel cycle engine output or crankshaft varies even during so-called steady-state operation of the engine, i.e., the shaft continuously accelerates and decelerates about the average speed of the shaft. The accelerations and decelerations are, of course for the most part, a result of power pulses from the engine cylinders. The pulses may be of uniform frequency and amplitude when cylinder charge density, air/fuel ratio and ignition are uniform. However, such uniformity does not always occur, thereby producing pulses which vary substantially in frequency and amplitude. Whether uniform or not, the pulses, which are herein referred to as torsionals, are transmitted through vehicle drivelines and are perceptible to vehicle passengers. The torsionals, which manifest themselves as vibrations are detrimental to drivelines, derogate passenger-ride quality, and may cause annoying body noises. An example of body noise, known as body boom, occurs when an engine is lugged; under such a condition engine torsionals may cause body components, such as sheet metal panels, to resonate. Still further, tip-in/tip-out torque pulses, produced by abrupt engine acceleration and/or deceleration, jerk the driveline and vehicle; such torque pulses are also referred to herein as torsionals.
Torsion isolators for attenuating and dampening driveline torsionals are well known in the prior art. Such isolators commonly employ a spring(s) and a damper. The spring(s) attenuate the torsionals and transmit positive and negative torque (i.e., engine and coast torque) between the vehicle engine and wheels. The damper controls the rate of spring flexing. Examples of such isolators may be seen by reference to U.S. Pat. Nos. 5,240,457; 5,234,377; 4,782,932 and published French patent application 2,611,013. These documents are incorporated herein by reference. The torsion isolator disclosed herein is considered to have several advantages over the above torsion isolators with respect to torsional attenuation and damping, cost, and weight or inertia.